KR20050038581A - Diode having vertical structure and method of manufacturing the same - Google Patents

Abstract

A light emitting diode includes a conductive layer, an n-GaN (105) layer on the conductive layer, an active layer (160) on the n-GaN layer, a p-GaN (140) layer on the active layer, and a p-electrode on the p-GaN layer. The conductive layer is an n- electrode.

Description

Diode having vertical structure and method of manufacturing the same

TECHNICAL FIELD The present invention relates to diodes, and more particularly, to a vertical structure light emitting diode (LED). Although the present invention is discussed with reference to GaN based light emitting diodes, the present invention can be used for many types of light emitting diodes, and can also be used in a wide range of applications including other types of diodes such as, for example, laser diodes.

Light emitting diodes, commonly referred to as "LEDs", are semiconductor devices that convert power into light emission. It is well known in the art that when electrons transition between their allowed energy levels in an atom or molecule, these energy transitions always carry a certain amount of energy gain or loss. In light emitting diodes, the generation or injection of electrons or hole currents through the diode junction creates this electronic transition, which in turn results in vibrational energy or light, or both. As is better known in the art, the color of light generated by light emitting diodes is generally determined by the nature of the semiconductor material, most notably by band gaps representing energy level differences between the valence and conduction bands of the individual atoms. It is limited.

Gallium nitride (GaN) has recently attracted much attention from researchers in the field of LEDs. This is because the wide direct bandgap nature of this material is very suitable for manufacturing blue LEDs. The blue LED has been considered the most difficult to manufacture among other red or green LEDs.

Accordingly, GaN-based optoelectronic device technology has been rapidly developed from the field of device research and development for commercialization since the devices were introduced to the market in 1994. For example, the efficiency of a GaN light emitting diode is superior to that of incandescent lighting and is equivalent to that of fluorescent lighting.

The market growth of GaN-based devices has been far ahead of the industrial market forecast each year. Despite this rapid growth, it is still too expensive to implement full color displays with GaN-based devices. This is because the manufacturing cost of the blue LED, which is essential for realizing a full color display, is too expensive compared to other visible LEDs. The wafer size for blue LED manufacturing is limited to 2 inches, and the process of growing a GaN epitaxial layer is more difficult than other semiconductor materials. Therefore, in using a full-color display using GaN LED, which is more efficient than currently available by reducing the manufacturing cost of the blue LED, at low cost, development of a technology for mass production without deterioration of performance is a major issue.

In general, GaN based LEDs are manufactured in a side structure using a sapphire substrate. This is because sapphire is a material that allows the GaN epitaxial layer to grow with fewer defects than other materials. Since sapphire is an electrical insulator, side type LEDs with both n and p metal contacts on the top face inevitably inject current into the MQW layer.

1 schematically illustrates a conventional side type LED device. Referring to FIG. 1, a conventional side type LED includes a substrate 100 such as sapphire. An optional buffer layer 120, for example made of gallium arsenide (GaN), is formed on substrate 100. An n-type GaN layer 140 is formed on the buffer layer 120. For example, an active layer such as a multi-quantum well (MQW) layer 160 of aluminum indium gallium nitride (AlInGaN) is formed on the n-type GaN layer 140. The p-type GaN layer 180 is formed on the active layer 160. The transparent conductive layer 220 is formed on the p-GaN layer 180. Transparent conductive layer 220 may be made of any suitable material, including, for example, Ni / Au or indium tin oxide (ITO). Then, a p-type electrode is formed on one side of the transparent conductive layer 220. P-type electrode 240 may be made of any suitable material, including, for example, Ni / Au, Pd / Au, Pd / Ni, and Pt. Pad 260 is formed on p-type electrode 240. The pad can be made of any suitable material, including for example Au. In order to form the n-electrode 250 and the pad 270, the transparent conductive layer 220, the p-GaN layer 180, the active layer 160, and the n-GaN layer 140 are all etched in one portion. do.

Since sapphire is an insulator, the n-GaN layer must be exposed to form n-metal contacts. Since GaN is not etched by the chemical etching method, a dry etching method is generally used. This is a serious problem because it requires additional lithography and stripping processes. In addition, plasma damage is frequently caused on the GaN surface during the dry etching process. In addition, the side device structure requires a large device size because two metal contacts must be formed at the top of the device. Moreover, the side structure device is susceptible to static electricity because the two metal electrodes are located close to each other. Thus, GaN-based LEDs with side structures may not be suitable for high pressure applications such as traffic signs or traffic lights.

Currently, GaN-based LEDs with vertical structures are being manufactured by Cree Laboratories using silicon carbide (SiC) substrates. However, due to the high manufacturing cost, LEDs with SiC substrates are not suitable for mass production. In addition, SiC is known in the art to be very sensitive to hydrogen atoms, which are subjected to organometallic chemical vapor deposition (MOCVD), the most common method of growing a GaN epitaxial layer considering the quality of epitaxial films. Present during epitaxial growth. In order to grow high quality GaN based epitaxial films, an additional process called "surface treatment" is needed. Moreover, GaN based LEDs with SiC substrates require an additional conductive buffer layer on the SiC substrate prior to growing the GaN epitaxial layer, which is unnecessary for side structure devices.

1 illustrates a conventional side structure LED.

2 illustrates another vertical structure LED in one embodiment of the present invention.

3 to 8 show manufacturing steps for forming a light emitting diode according to the present invention.

9 shows another embodiment of the vertical structure LED of the present invention.

Accordingly, the present invention relates to a method of manufacturing a simple vertical structure LED for mass production, which substantially eliminates one or more problems due to the limitations and disadvantages of the related art.

An advantage of the present invention is to increase the number of LED devices manufactured within the limited wafer area.

Another advantage of the present invention is that the LED device has a simple manufacturing process step.

Additional features and advantages of the invention will be set forth in detail in the description which follows, and in part will be obvious from the description, and will be learned by practice of the invention. The objects and other advantages of the present invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

In accordance with the object of the present invention and in order to achieve the various advantages described above, as embodied and comprehensively described, a method of manufacturing a light emitting diode comprises a buffer GaN by vapor phase epitaxy (VPE) on a sapphire substrate. Forming a layer; Forming an n-GaN epitaxial layer by MOCVD on the buffer GaN; forming a multi-quantum well (MQW) layer on the n-GaN epitaxial layer; Forming a p-GaN layer on the MQW layer by MOCVD; Separating the sapphire substrate from the other layers; forming p and n metal contacts; forming a metal transparent contact on a side of the p-GaN layer; And forming a metal pad on the p-GaN layer.

In another aspect, a method of manufacturing a light emitting diode comprises: forming a buffer GaN layer by VPE on a sapphire substrate; Forming a undoped GaN layer by VPE over the buffer GaN layer; Forming an n-GaN layer by VPE over the undoped GaN layer; Forming an n-GaN epitaxial layer by MOCVD over n-GaN grown by VPE; forming an MQW layer over the n-GaN epitaxial layer; Forming a p-GaN layer over the MQW layer by MOCVD; Separating the sapphire substrate from the other layers; forming p and n metal contacts, forming a metal transparent contact over the p-GaN layer; And forming a metal pad over the p GaN layer.

In another aspect, a method of manufacturing a light emitting diode comprises: forming a buffer GaN layer by VPE on a sapphire substrate; Forming an n-GaN epitaxial layer by MOCVD over the buffer GaN layer; forming an MQW layer over the n-GaN epitaxial layer, forming a p-AlGaN clad layer over the MQW layer by MOCVD; Forming a p-GaN conductive layer on the p-AlGaN layer by MOCVD; Separating the sapphire substrate from the other layers; forming p and n contacts; forming a metal transparent contact on the p-GaN layer; And forming a metal pad on the p-GaN layer.

In another aspect, a method of manufacturing a light emitting diode comprises: forming a buffer GaN layer by VPE on a sapphire substrate; Forming a undoped GaN layer by VPE over the buffer GaN layer; Forming an n-GaN layer by VPE over the undoped GaN layer; Forming an n-GaN epitaxial layer by MOCVD over n-GaN grown by VPE; forming an MQW layer over the n-GaN epitaxial layer; Forming a p-AlGaN clad layer on the MQW layer by MOCVD; Forming a p-GaN conductive layer on the p-AlGaN layer by MOCVD; Separating the sapphire substrate from the other layers; forming a metal transparent contact over the p-GaN layer; And forming a metal pad over the p-GaN layer.

It is to be understood that the foregoing general description and the following detailed description of the invention are exemplary and explanatory and are intended to illustrate the invention of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are provided to better understand the present invention and which form part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

Hereinafter, the present invention will be described in detail. Examples of the invention are illustrated in the accompanying drawings.

2 illustrates a vertical structure light emitting diode according to an embodiment of the present invention. Referring to FIG. 2, the vertical LED includes an n-contact 500. A buffer layer 105 made of GaN is over the n-contact 500. An n-GaN layer 140 is over the buffer layer 105. For example, an active layer 160 made of a multi-quantum well (MQW) layer containing AlInGaN is on the n-GaN layer 140. The p-GaN layer 180 is over the active layer 160. The p-contact layer 220 is over the p-GaN layer 180. P-electrode 240 and pad 260 are formed over p-contact layer 220.

In the LED shown in FIG. 2, the n-contact 500 can serve two functions. First, the n-contact portion 500 functions as an electrically conductive material. Second, the n-contact can also serve to reflect photons emitted from the active layer 160 to the n-contact 500. If this is not done, this increases the brightness of the LED because photons that are absorbed or consumed in some other way are reflected off the n-contact 500 and emit light. A material having good reflective properties such as a mirror can be used as the n-contact 500. One of the examples above is a polished aluminum layer. The reflective properties are described in detail in the currently pending application entitled "Diode with High Brightness and Method thereof", filed on July 17, 2001 by Inventive Iron and filed by the same assignee as the present application. This application is hereby incorporated by reference in its entirety. Hereinafter, the material for the n-contact portion 500 will be described in detail.

The advantage of the vertical structure LED of the present invention is that the size of the LED chip is very small compared with the side structure of the conventional LED. Due to the small chip size, much more chips can be formed on wafers of the same size, such as sapphire. Moreover, as will be described in detail below, the number of process steps for forming the vertical structure LED of the present invention is reduced. 3 to 8 schematically illustrate a process for manufacturing a vertical structure GaN based light emitting diode (LED) according to the present invention. To manufacture GaN-based LEDs, sapphire substrates have been commonly used because sapphire is very stable and relatively inexpensive. The epitaxial layer quality of various GaN layers grown on sapphire substrates is superior to other substrate materials due to thermal stability and similar crystal structure of GaN.

Referring to FIG. 3, a buffer layer 120 is formed on a transparent substrate 100, preferably a sapphire substrate. As a result, the buffer layer 120 that replaces the function of the sapphire substrate 100 may be formed of one, two, or three layers. For example, the buffer layer 120 may have only an n-GaN layer grown by the VPE. For two buffer layers, the first layer 110 of the GaN layer is grown on the sapphire substrate, for example by VPE, and the second layer 120 of the n-GaN layer, on the GaN layer 110 by VPE, for example. Is grown on. For the three buffer layers, the first layer 110 of the GaN layer is grown on the sapphire substrate, for example by VPE, and the second layer 130 of the undoped GaN layer is the first layer of the GaN layer, for example by VPE. Grown on layer 110, a third layer 120 of n-GaN layer is grown on GaN layer 130, which is not doped, for example by VPE.

GaN layer 130 may be formed to have a thickness in the range of about 40-50 nm. The undoped GaN layer 130 may be formed to have a thickness in the range of about 30 to 40 μm. The n-GaN layer 120 may be formed to have a thickness of about 1 to 2 μm. For n-GaN 120, a silene gas (SiH ₄ ) may be used as the n-type dopant.

Referring to FIG. 4, an n-type epitaxial layer such as n-GaN 140 is epitaxially grown on the buffer layer 120 by organometallic chemical vapor deposition (MOCVD). Advantageously, a chemical cleaning step (not shown) of the buffer layer 120 grown by the VPE method is added before growing the n-GaN layer 140 by the MOCVD method, so as to produce good quality n-GaN epi. The taxi layer 140 may be obtained. In this example, n-GaN layer 140 was doped with silicon (Si) at a doping concentration of about 10 ¹⁷ cm ⁻³ or more.

Referring to FIG. 5, an active layer 160, such as an AlInGaN multi-quantum well (MQW) layer, is formed on the n-GaN layer 140 by the MOCVD method. Active layer 160 may be any suitable structure, including a single quantum well layer or a double heterostructure. In this example, the amount of indium (In) determines whether the diode is green or blue. For LEDs with blue, about 22% of indium can be used. For LEDs with green color, about 40% of indium can be used. The amount of indium used may vary depending on the required wavelength of blue or green. Thus, the p-GaN layer 180 is formed by MOCVD, for example, using CP ₂ Mg as the p-type dopant on the active layer 160. In this example, the p-GaN layer 180 was doped with magnesium (Mg) at a doping concentration of about 10 ¹⁷ cm ⁻³ or more.

With reference to FIG. 6A, the sapphire substrate 100 is preferably separated from other layers by a laser lift-off method. Other suitable techniques may be used to separate the sapphire substrate 100 from other layers. The other layers include a buffer layer 120, an n-GaN layer 140, an active layer 160, and a p-GaN layer 180. By removing the sapphire substrate 100, which is an electrical insulator, from the device, an n-metal contact can be formed under the n-type GaN buffer layer 120, which is an electrical conductor.

Referring to FIG. 6B, after the substrate 100 is removed, the layers under the buffer layer 120 may also be removed using, for example, dry etching. This step will expose the n-GaN buffer layer 120 to be electrically attached to the n-contact 500 as shown in FIG. 8.

Referring to FIG. 8, a transparent conductive layer 220 is formed on the p-GaN layer 180. The transparent conductive layer 220 may be made of any suitable material, including, for example, indium tin oxide (ITO). The p-type electrode 240 is formed on the transparent conductive layer 220. An n-type electrode 500 is formed on the lower end of the buffer layer 120. P-type electrode 240 may be made of any suitable material, including, for example, Ni / Au, Pd / Au, Pd / Ni, and Pt. The n-type electrode 500 may be made of any suitable material, including for example Ti / Al, Cr / Au and Ti / Au. Pad 260 is formed on p-type electrode 240. Pad 260 may be made of any suitable material, including, for example, Au. Pad 260 may have a thickness of about 0.5 μm or more. Unlike the p-type electrode 240, the n-type electrode 500 does not require a pad. However, it can be preferably used.

9 illustrates another embodiment in which a cladding layer 170 is formed between the p-GaN layer 180 and the active layer 160. Clad layer 170 is preferably formed of p-AlGaN by MOCVD using CP ₂ Mg as p-type dopant. Clad layer 170 enhances the performance of the LED device.

According to the present invention, there are many advantages over both conventional side and vertical GaN based LEDs. Compared with conventional side structure GaN based LEDs, the manufacturing process according to the present invention increases the number of LED devices fabricated on a given wafer size since there are no n-metal contacts on top of the device. For example, the size of the device can be reduced from 250 × 250 μm to about 160 × 160 μm or less. By not having n-metal contacts on top of the device or on top of the substrate, according to the invention, the manufacturing process can be very simplified. This is because no additional photolithography or etching process is required to form the n-type contacts, and there is no plasma damage often applied on the n-GaN layer in conventional side structure GaN based LEDs. Moreover, LED devices made in accordance with the present invention are more resistant to static electricity, which makes LEDs more suitable for high pressure applications than conventional side structure LED devices.

In general, the VPE deposition method is much simpler and requires less time to grow the epitaxial layer to a predetermined thickness than the MOCVD deposition method. Thus, the manufacturing process according to the present invention is simpler than the conventional vertical GaN based LED in that the manufacturing process does not need to grow buffer and n-GaN layers by the MOCVD method, and the process time is much shorter. For example, as a whole, the number of manufacturing processes is reduced from 28 steps of the conventional method to 15 steps of the present invention. In addition, manufacturing costs are significantly reduced compared to conventional vertical structure GaN based LEDs using silicon carbide (SiC), which can be 10 times more expensive than sapphire substrates. Moreover, the method according to the present invention significantly improves metal adhesion between the junction pad and the n and p contacts over conventional vertical structure GaN based LEDs.

With the present invention, it becomes possible to mass-produce GaN based LEDs at low cost without sacrificing or changing the desirable properties of the LEDs. Moreover, the vertical structure of the LED of the present invention with a reflective bottom n-junction improves the brightness of the LED. The present invention can be applied to other suitable devices as well as blue, green, red, and white LEDs currently available.

Although the invention has been described in detail with reference to GaN technology diodes, the invention is readily applicable to other types of diodes, including laser diodes including vertical cavity surface emitting lasers (VCSELs) and red LEDs. Can be.

It will be apparent to those skilled in the art that various modifications and variations can be made within the present invention without departing from the spirit and scope of the invention. Accordingly, it is intended that the modifications and variations of this invention fall within the scope of the appended claims and their equivalents.

Included in the foregoing.

Claims (63)

Conductive layer; An n-GaN layer over the conductive layer; an active layer over the n-GaN layer; A p-GaN layer over the active layer; And a p-electrode on the p-GaN layer, Wherein the conductive layer is an n-electrode. The method of claim 1, A light emitting diode, wherein the conductive layer also serves as a reflective layer to reflect light from the active layer. The method of claim 1, Light-emitting diode, characterized in that the conductive layer is made of aluminum. The method of claim 1, The conductive layer includes a metal selected from the group consisting of aluminum, gold, palladium, titanium, indium, nickel and platinum. The method of claim 4, wherein Wherein the conductive layer comprises aluminum having a concentration of about 99.999% or greater. The method of claim 1, A light emitting diode, wherein the conductive layer comprises about 3000 kV of aluminum. The method of claim 1, A light emitting diode, wherein the conductive layer completely covers one side of the n-GaN layer. The method of claim 1, A light emitting diode further comprising a buffer layer between the conductive layer and the n-GaN layer. The method of claim 1, Light-emitting diode, characterized in that the buffer layer comprises n-GaN. The method of claim 1, and a p-transparent contact portion between the p-electrode and the p-GaN layer. The method of claim 10, and the p-transparent contact portion comprises indium-tin-oxide. The method of claim 1, and a metal pad on the p-electrode. The method of claim 12, A light emitting diode, wherein the metal pad is about 5000 mW or more. The method of claim 12, The metal pad includes Au. The method of claim 1, Light-emitting diode, characterized in that the conductive layer comprises Ti and Al (Ti / Al). The method of claim 1, The conductive layer is a light emitting diode comprising a material selected from the group consisting of Ti / Al, Cr / Au and Ti / Au. The method of claim 1, The p-electrode comprises Ni and Au (Ni / Au). The method of claim 1, p-electrode comprises a material selected from the group consisting of Ni / Au, Pd / Au, Pd / Ni and Pt. The method of claim 1, Light-emitting diode, characterized in that the active layer comprises AlInGaN. The method of claim 1, The active layer comprises at least one of a quantum well layer (quantum well layer) and a double hetero structure (double hetero structure). The method of claim 1, A light emitting diode, characterized in that the quantum layer comprises multiple quantum layers. The method of claim 1, A light emitting diode further comprising a cladding layer between the p-GaN layer and the active layer. A first electrode; An n-type layer and a p-type layer on the first electrode; an active layer between the n-type layer and the p-type layer; And a second electrode in contact with the p-type layer, The first electrode is in contact with the n-type layer and serves as a reflective layer to reflect light from the active layer. The method of claim 23, And the reflective layer completely covers the n-type layer. The method of claim 23, The light emitting diode, characterized in that the reflective layer comprises aluminum. The method of claim 25, Light-emitting diodes, characterized in that aluminum has a concentration of about 99.999% or more. The method of claim 23, A light emitting diode further comprising a buffer layer between the first electrode and the n-type layer. The method of claim 27, Light-emitting diode, characterized in that the buffer layer comprises n-GaN. The method of claim 23, The active layer includes at least one of a quantum well layer and a double hetero structure. The method of claim 23, The quantum layer is a light emitting diode comprising a multi-quantum layer. Forming a first n-GaN layer on the substrate; Forming an active layer on the first n-GaN layer; Forming a p-GaN layer on the active layer; Separating the substrate from the first n-GaN layer; forming an n-type contact layer on the n-GaN layer; forming a p-electrode on the p-GaN layer, The n-type contact layer acts as a reflective layer to reflect light from the active layer. The method of claim 31, wherein and the p-electrode is formed before the step of separating the substrate. The method of claim 31, wherein And forming a second n-GaN layer between the substrate and the first n-GaN layer. The method of claim 33, wherein And the second n-GaN is formed using organometallic chemical vapor deposition (MOCVD). The method of claim 31, wherein Diode manufacturing method characterized in that the substrate comprises sapphire. The method of claim 31, wherein And the substrate is separated from the first n-GaN using a laser. The method of claim 31, wherein and forming a transparent conductive layer between the p-electrode and the p-GaN layer. A first electrode having an epitaxially grown GaN layer on one side; Second electrode; An active layer between the first and second electrodes, The first electrode is a reflective layer that reflects light from the active layer. The method of claim 38, Illuminating device, characterized in that the reflective layer maximizes the light emitted from the diode. Forming a second GaN layer on the substrate having the first GaN layer; Forming an active layer on the second GaN layer; Forming a third GaN layer on the active layer; Separating the substrate in the first GaN layer; And Forming a first electrode on the separated first GaN layer; The method of claim 1, wherein the first electrode is a reflective layer that reflects light from the active layer. The method of claim 40, And a second GaN layer is formed on the first GaN layer using organometallic chemical vapor deposition (MOCVD). The method of claim 40, A method for fabricating a diode, wherein a first GaN layer is epitaxially grown on a substrate. The method of claim 40, Diode manufacturing method characterized in that the substrate is separated using a laser. The method of claim 40, 12. A method of fabricating a diode, wherein the active layer comprises multiple quantum wells. The method of claim 40, Diode manufacturing method characterized in that the substrate comprises sapphire. The method of claim 40, Diode manufacturing method, characterized in that the first electrode comprises aluminum. A reflective conductive layer of a first polarity; A first GaN layer of a first polarity on the reflective conductive layer; An active layer on the first GaN layer; A second GaN layer of second polarity on the active layer; And A light emitting diode comprising an electrode of a second polarity on the second GaN layer. The method of claim 47, The light emitting diode further comprising a transparent conductive layer between the second GaN layer and the electrode. The method of claim 47, The reflective layer includes a conductive material and serves as an electrode of a first polarity. The method of claim 47, A light emitting diode, wherein the reflective layer has an area substantially the same as that of the first GaN layer. The method of claim 47, Wherein the first polarity is n-type and the second polarity is p-type. The method of claim 47, A light emitting diode further comprising a cladding layer between the active layer and the second GaN layer. The method of claim 52, wherein The cladding layer comprises AlGaN. The method of claim 47, The active layer includes at least one of a quantum well layer and a double hetero structure. The method of claim 47, The quantum layer is a light emitting diode comprising a multiple quantum well layer. forming n-GaN on the first surface of the n-GaN buffer layer; forming an AlInGaN active layer on the n-GaN layer; Forming a cladding layer on the AlInGaN active layer; forming a p-GaN layer on the p-AlGaN clad layer; forming a p-type electrode on the p-GaN layer; forming a transparent conductive layer on the p-GaN layer; And forming an n-type electrode on the second surface of the n-GaN buffer layer. The method of claim 56, wherein The cladding layer comprises p-AlGaN. The method of claim 56, wherein The cladding layer is formed by organic metal chemical vapor deposition (MOCVD). A buffer layer having a first and a second surface; An n-GaN layer on the first surface of the buffer layer; an active layer on the n-GaN layer; A p-GaN layer on the active layer; a p-electrode on the p-GaN layer; And And a n-electrode on the second surface of the buffer layer. The method of claim 59, And a cladding layer formed between the active layer and the p-GaN layer. The method of claim 60, And wherein the cladding layer comprises p-AlGaN. The method of claim 59, And a metal transparent contact portion is formed on the p-GaN layer. The method of claim 62, And a metal pad is formed on one side of the metal transparent contact portion.